1. Field of the Invention
The present invention relates to materials which are particularly suitable as highly active catalysts for the decomposition of chlorofluorocarbons (flons) to hydrofluoric acid, hydrochloric acid and carbon dioxide, and are characterized by being easy to produce into catalysts and providing for easy recovery of its catalytically useful components.
2. Description of the Prior Art
Investigations into methods for the decomposition of flons had previously been unnecessary and hence were seldom performed. It has been known that they decompose by burning at high temperatures, such as 800.degree. C., in an incinerator. According to recent investigations of the catalytic decomposition of flons on metal oxides, decomposition of flons occurred on zeolite at temperatures of from 300.degree.-500.degree. C.
In general, ordinary alloys are crystalline in their solid state. However, rapid quenching of some alloys having specific compositions in the liquid state gives rise to the solidification of an amorphous structure. These alloys are called amorphous alloys. The amorphous alloys are single phase alloys supersaturated with various elements and have significantly high mechanical strength in comparison with conventional industrial alloys. Some amorphous alloys with specific compositions have a variety of superior characteristics including extremely high corrosion resistance that cannot be obtained in ordinary crystalline alloys.
One of the present inventors applied the teachings of Japanese Patent Application No. 123111/85 regarding amorphous alloy electrode materials, which contain Ni, Ta and platinum group elements as essential components and are suitable as an anode for oxygen production by the electrolysis of acidic aqueous solutions because of their high activity for oxygen evolution.
Japanese Patent Application No. 123111/85 discloses:
(1) Amorphous alloy electrode materials which comprise 25 to 65 at % Ta, 0.3 to 45 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, and more than 30 at % Ni.
(2) Amorphous alloy electrode materials which comprise 25 to 65 at % Ta and at least one element selected from the group of Ti, Zr and Nb, Ta being present in an amount of at least 20 at %, 0.3 to 45 of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, and more than 30 at % Ni.
Three of the present inventors have further developed surface activated amorphous alloy electrode materials which are suitable for the electrolysis of aqueous solutions and consist of Ni, very small amounts of platinum group metals and at least one element selected from the group of Ti, Zr, Nb and Ta, and their activation methods in Japanese Patent Application Nos. 169764/85, 169765/85 and 169767/85. They further applied the teachings of Japanese Patent Application No. 169766/85 regarding surface-activated supersaturated solid solution alloy electrode materials for electrolysis of aqueous solutions and their activation methods.
Japanese Patent Application No. 169764/85 discloses:
(1) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % of Nb, 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, and the balance substantially being Ni, used for the electrolysis of aqueous solutions.
(2) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % Nb and at least one element selected from the group of Ti, Zr and less than 20 at % of Ta, Nb being present in an amount of at least 10 at %, and 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, and the balance substantially being Ni, used for the was applied for electrolysis of aqueous solutions.
(3) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % of Nb, 0.01 to 10 at % of at least one element selected from the group consisting of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the substantial balance of Ni, used for the electrolysis of aqueous solutions.
(4) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % Nb and at least one element selected from the group consisting of Ti, Zr and less than 20 at % of Ta, Nb being present in an amount of at least 10 at %, and 0.01 to 10 at % least one element selected from the group of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the balance substantially being Ni, used for the electrolysis of aqueous solutions.
(5) A method for activating amorphous alloys for electrodes characterized by the immersion of the above-mentioned amorphous alloy electrode materials into corrosive solutions for surface enrichment of platinum group elements as a result of preferential dissolution of Ni, Nb, Ta, Ti and Zr.
Japanese Patent Application No. 169765/85 discloses:
(1) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % of Ta, 0.01 to 10 at % of at least one element selected from the group consisting of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the balance substantially being 20 at % or more Ni, used for electrolysis of aqueous solutions.
(2) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % Ta and at least one element selected from the group of Ti, Zr and Nb, Ta being present in an amount of at least 20 at %, 0.01 to 10 at % of at least one element selected from the group of Ru, Ph, Pd, Ir and Pt, less than 7 at % of P and the substantial balance being 20 at % or more Ni, used for the electrolysis of aqueous solutions.
(3) A method for activating amorphous alloys for electrodes characterized by the immersion of the above-mentioned amorphous alloy electrode materials into corrosive solutions for surface enrichment of platinum group elements as a result of preferential dissolution of Ni, Nb, Ta, Ti and Zr.
Japanese Patent Application No. 169767/85 discloses:
(1) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % Ta and at least one element selected from the group of Ti and Zr, Ta being present in an amount of from 5 to less than 20 at %, and 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, the substantial balance being Ni, used for the electrolysis of aqueous solutions.
(2) Surface-activated amorphous alloy electrode materials consisting of 25 to 65 at % Ta and at least one element selected from the group of Ti and Zr, Ta being present in an amount of from 5 to less than 20 at %, and 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the balance substantially being 20 at % or more Ni, used for the electrolysis of aqueous solutions.
(3) A method for activating amorphous alloys for electrodes characterized by immersing the above-mentioned amorphous alloy electrode materials into corrosive solutions for surface enrichment of platinum group elements as a result of the preferential dissolution of Ni, Ta, Ti and Zr.
Japanese Patent Application No. 169766/85 discloses:
(1) Surface-activated supersaturated solid solution alloy electrode materials consisting of 20 to less than 25 at % of at least one element selected from the group of Nb and Ta, 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt and the balance substantially being Ni, used for the electrolysis of aqueous solutions.
(2) Surface-activated supersaturated solid solution alloy electrode materials consisting of 20 to less than 25 at % of at least one element selected from the group of Nb and Ta, 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the substantial balance being Ni, used for the electrolysis of aqueous solutions.
(3) Surface-activated supersaturated solid solution alloy electrode materials consisting of 20 to less than 25 at % of at least one element selected from the group of Ti and Zr and 5 at % or more of at least one element selected from the group of Nb and Ta, 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt and the balance substantially being Ni, used for the electrolysis of aqueous solutions.
(4) Surface-activated supersaturated solid solution alloy electrode materials consisting of 20 to less than 25 at % of at least one element selected from the group of Ti and Zr and 5 at % or more of at least one element selected from the group of Nb and Ta, 0.01 to 10 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, less than 7 at % of P and the balance substantially being Ni, used for the electrolysis of aqueous solutions.
(5) A method for activating supersaturated solid solution alloys for electrodes characterized by immersing the above-mentioned supersaturated solid solution alloy electrode materials into corrosive solutions for surface enrichment of platinum group elements as a result of the preferential dissolution of Ni, Nb, Ta, Ti and Zr.
Furthermore, the present inventors presented surface-activated amorphous alloys for methanol fuel cell in Japanese Patent Application No. 154570/86.
Japanese Patent Application No. 154570/86 discloses:
(1) Surface-activated amorphous alloys for methanol fuel cells, consisting of 20 to 80 at % of at least one element selected from the group of Ti and Zr, 0.5 to 20 at % of Pt and the balance substantially being 10 at % or more of at least one element selected from the group of Ni and Co.
(2) Surface-activated amorphous alloys for methanol fuel cells consisting of 20 to 80 at % of at least one element selected from the group of Ti and Zr, 0.5 to 20 at % of Pt, at most 10 at % (at most the same at % as Pt if Pt is at most 10 at %) of at least one element selected from the group of Ru, Rh, Pd, Ir, Tl, Si, Ge, Sn, Pb and Bi and the balance substantially being 10 at % or more of at least one element selected from the group of Ni and Co.
(3) Surface-activated amorphous alloys for methanol fuel cells, consisting of 20 to 70 at % of at least one element selected from the group of Nb and Ta, 0.5 to 20 at % of Pt, and the balance substantially being at least one element selected from the group of Ni and Co.
(4) Surface-activated amorphous alloys for methanol fuel cells, consisting of 20 to 70 at % of at least one element selected from the group of Nb and Ta, 0.5 to 20 at % of Pt, at most 10 at % (at most the same at % as Pt if Pt is at most 10 at %) of at least one element selected from the group of Ru, Rh, Pd, Ir, Tl, Si, Ge, Sn, Pb and Bi, and the balance substantially being 10 at % or more of at least one element selected from the group of Ni and Co.
(5) Surface-activated amorphous alloys for methanol fuel cells consisting of 20 to 80 at % of at least one element selected from the group of Ti and Zr and at most 70 at % of at least one element selected from the group of Nb and Ta, 0.5 to 20 at % of Pt, and the balance substantially being 10 at % or more of at least one element selected from the group of Ni and Co.
(6) Surface-activated amorphous alloys for methanol fuel cell, consisting of 20 to 80 at % of at least one element selected from the group of Ti and Zr and at most 70 at % of at least one element selected from the group of Nb and Ta, 0.5 to 20 at % of Pt, at most 10 at % (at most the same at % as Pt if Pt is at most 10 at %) of at least one element selected from the group of Ru, Rh, Pd, Ir, Tl, Si, Ge, Sn, Pb and Bi, and the balance substantially being 10 at % or more of at least one element selected from the group of Ni and Co.
In order to overcome the high operation temperatures of catalysts consisting of platinum group elements supported on ceramics used in the purification of exhaust gases from plants and vehicles, in addition to the difficulty of recovering platinum group elements, three of the present inventors investigated catalysts capable of operating at low temperatures, such as the beginning of combustion, in addition to being easy to recover, and invented catalysts for the purification of exhaust gases by the reaction of carbon monoxide with nitrogen oxides in exhaust gases as Japanese Patent Application No. 262986/89.
The Japanese Patent Application No. 262986/89 discloses:
(1) Surface-activated catalysts for purifying exhaust gases, consisting of 20 to 70 at % of at least one element selected from the group of Nb and Ta, 0.5 to 20 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, and the balance substantially being at least one element selected from the group of Ni and Co.
(2) Surface-activated catalysts for the purification of exhaust gases, consisting of 20 to 80 at % of at least one element selected from the group of Ti and Zr, 0.5 to 20 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt, and the balance substantially being at least 10 at % of at least one element selected from the group of Ni and Co.
(3) Surface-activated catalysts for the purification of exhaust gases, consisting of 20 to 80 at % of at least one element selected from the group of Ti and Zr and at most 70 at % of at least one element selected from the group of Nb and Ta, 0.5 to 20 at % of at least one element selected from the group of Ru, Rh, Pd, Ir and Pt and the balance substantially being at least 10 at % of at least one element selected from the group of Ni and Co.
Until the year 2000, the production and use of the 5 worst flons, which destruct ozonosphere and induce the greenhouse effect, will be prohibited. They may be substituted by other flons. Current industries are using large amounts of different flons. It is, therefore, necessary to develop a technique by which used flons can be converted to hydrofluoric acid, hydrochloric acid and carbon dioxide for re-use without consumption of a large amount of energy.
In view of the above discussion, there has been a strong demand for highly active and easily recoverable catalysts for converting flons at low temperatures and with a low consumption of energy.